Voyager 2, one of the greatest success stories in space exploration, continues to venture into interstellar space, far beyond the confines of our Solar System. However, after 47 years of operation, the probe encounters inevitable challenges. The reduction in its energy forces engineers to gradually turn off some of its scientific instruments.
Voyager 2: a journey beyond the heliosphere
Voyager 2 left Earth on August 20, 1977, a few weeks before its twin Voyager 1. Since then, it has traveled more than 20.5 billion kilometers and crossed the boundary of the Solar System in November 2018. This landmark moment is known as the crossing of the heliopause, the boundary where the solar wind, a stream of charged particles emitted by our star, ceases to dominate and where begins interstellar space.
Once this threshold was crossed, Voyager 2 became one of only two probes to have explored interstellar space, the other being Voyager 1 which crossed this same boundary in 2012. Since then, Voyager 2 has continued to collect valuable information on this unknown environment, well beyond the direct influence of the Sun.
Valuable instruments, but limited energy
To continue exploring interstellar space, Voyager 2 still uses four scientific instruments. However, as the years pass, the probe’s power diminishes, as it is powered by decaying plutonium, an energy source that loses about four watts each year. As a result, engineers must make difficult choices about which instruments to leave on and which to turn off to extend the life of the mission.
On September 26, the NASA team made the decision to turn off plasma science instrument of Voyager 2. This instrument composed of four cups measured the quantity of plasma, a fluid of charged particles, interacting with the probe. Three of the cups, oriented towards the Sun, had already stopped collecting data since the spacecraft crossed the heliopause. The fourth cup, oriented towards interstellar space, continued to provide information, but its readings were limited to a single useful collection every three months, when the probe rotated on its axis.
Given these constraints, NASA decided that this instrument could be sacrificed to save energy and thus allow other instruments to operate for longer. With only four instruments remaining, it is now essential to save every watt to allow Voyager 2 to continue operating at least until the 2030s. At this point, it is expected that the probe will only be able to power a single scientific instrument.
